Mesoporous Silica Sieve Research Articles

Recent Progress on Functionalized Nanoporous Heteropoly Acids: From Synthesis to Applications.

Functionalized nanoporous heteropoly acids (HPAs) have garnered significant attention in recent years due to their enhanced surface area and porosity, as well as their potential for low-cost regeneration compared to bulk materials. This review aims to provide an overview of the recent advancements in the synthesis and applications of functionalized HPAs. We begin by introducing the fundamental properties of HPAs and their unique structure, followed by a comprehensive overview of the various approaches employed for the synthesis of functionalized HPAs, including salts, anchoring onto supports, and implementing mesoporous silica sieves. The potential applications of functionalized HPAs in various fields are also discussed, highlighting their boosted performance in a wide range of applications. Finally, we address the current challenges and present future prospects in the development of functionalized HPAs, particularly in the context of mesoporous HPAs. This review aims to provide a comprehensive summary of the recent progress in the field, highlighting the significant advancements made in the synthesis and applications of functionalized HPAs.

Humidity-resistant hydrogen sensors based on rare-earth-doped tin dioxide nanofibers with hydrophobic mesoporous silica sieve encapsulation

Air humidity is a major factor that degrades the performance and long-term stability of metal-oxide-semiconductor (MOS) based gas sensors. In this work, we propose an encapsulation strategy by coating a mesoporous silica molecular sieve (SBA-15) on rare earth doped tin oxide (RE-SnO2) nanofibers for humidity-resistant hydrogen detection. In this design, the hydrophobic SBA-15 sieve layer effectively blocks the water molecules without affecting hydrogen diffusion, while the RE dopant greatly improves the responsivity and lowers down the operating temperature of the sensors, As a result, the Er-SnO2/SBA-15 and Tb-SnO2/SBA-15 sensors respectively show the maximum response values of 27.71 and 33.68 (to 10 ppm hydrogen at 280 °C, 4.67 and 5.67 times that of the bare SnO2 ones, respectively), short response/recovery time (< 1.0 s / < 1.0 s), as well as a low limit of detection for hydrogen (200 ppb) and a good gas selectivity. Under the protection of the SBA-15 sieve layer, the response retention of the sensors is significantly improved when the humidity increases from 25% to 85% RH (Er-doping, from 38.8% to 60.0%; Tb-doping, form 25.6–57.8%). Besides, further analysis on enhancement mechanism of response indicates that the SBA-15 coating contribute about 1/3 of the response enhancements via its own hydrogen physical adsorption capacity and the induced oxygen vacancies during the calcination processes.

Effect of Zirconia on Pd–Pt Supported SBA-15 Catalysts for the Oxidation of Methane

A series of methane oxidation catalysts were prepared by doping Santa Barbara Amorphous-15 (SBA-15), a highly mesoporous silica sieve, with varying amounts of Zr (5, 10, and 15 wt%) and loading with 2 wt% Pd and 4 wt% Pt. The catalysts were characterized using various techniques, including BET, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and H2-temperature programmed reduction (H2-TPR). Fresh and aged catalysts were evaluated for methane oxidation. Aging was performed using a simulated lean burn natural gas (NG) engine exhaust containing water vapor (10% vol) and sulfur (10 ppm). It was found that the catalyst with 15 wt% zirconia was the most active and stable of the series, exhibiting the lowest T50 of 481 °C after 40 h of aging. The Pd–Pt catalyst loaded on pure SBA-15 had a T50 of 583 °C after aging, which was 102 °C higher than that of the Pd–Pt catalyst with 15 wt% Zr. The results suggest that the increased performance was due to the higher amount of reducible PtOx species in the proximity of ZrO2 and the sulfur scavenging effect of zirconia, which protected the active metals from forming inactive sulfur complexes. Overall, the Pd–Pt catalyst with 15 wt% Zr loaded on SBA-15 demonstrated excellent methane oxidation activity, hydrothermal stability, and sulfur resistance and can be considered a viable candidate for reducing the methane slip from a lean burn NG engine exhaust.

Growth of ZrO2 films on mesoporous silica sieve via atomic layer deposition

The atomic layer deposition of ZrO2 thin films over the mesopores of a mesoporous silica sieve, SBA-15 (Santa Barbara Amorphous-15), using the tetrakis(dimethylamino)zirconium(IV) (TDMAZ) as ZrO2 precursor was tested and characterized using N2 adsorption-desorption isotherms, taking advantage of the well-defined shape and size distribution of the pores in the SBA-15. Three samples were prepared, using 2, 4, and 6 deposition cycles to control the thickness of the films. It was determined that, as the average size of the pores decreased (with the increasing number of cycles), their size distribution remained narrow, indicating a homogeneous distribution of the ZrO2 throughout the surfaces of the SBA-15 pores. This conclusion was confirmed by transmission electron microscopy and X-ray photoelectron spectroscopy. The deposition rate appears to slow down after 4 cycles, an observation that we explain by different chemisorption properties of TDMAZ molecules over SBA-15 and ZrO2 surface and by relating the kinetic diameter of TDMAZ with the pore diameter of SBA-15 after 4 deposition cycles: mass transport limitations have become significant at this point. They may be affected by complex factors like electronic effects caused by exposed ZrO2 surface and the multi-directional adsorption of precursor molecules in the pore walls.

Effects of Pore Size and Crosslinking Methods on the Immobilization of Myoglobin in SBA-15.

A series of stable mesoporous silica sieves (SBA-15) with different pore sizes (9.8, 7.2, and 5.5 nm) were synthesized using a hydrothermal method. The resulting mesoporous material was then utilized for protein immobilization using myoglobin (Mb) as the target protein. The effects of pore size and adsorption methods on the immobilization efficiency of Mb in a mesoporous material were studied. The SBA-15 with a pore size of 7.2 nm showed the best loading capacity, reaching 413.8 mg/g. The SBA-15 with a pore size of 9.8 nm showed the highest retained catalytic ability (92.36%). The immobilized enzyme was more stable than the free enzyme. After seven consecutive assay cycles, Mb adsorbed by SBA-15 (Mb/SBA-15) and Mb adsorbed by SBA-15 and crosslinked with glutaraldehyde (Mb/G/SBA-15) retained 36.41% and 62.37% of their initial activity, respectively.

Removal of Brilliant Red dye (Brilliant Red E-4BA) from wastewater using novel Chitosan/SBA-15 nanofiber

An environmental-friendly adsorbent composed of chitosan nanofibers modified by mesoporous silica sieve (CTS-SBA-15) was synthesized via an electrospinning technique and used to remove of brilliant Red dye from a wastewater solution. Characterization of the synthesized nanofibers using Fourier transform infrared (FT-IR), X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses revealed that the chitosan nanofibers were effectively modified with mesoporous silica sieve (SBA-15). The effects of some adsorption parameters such as pH, adsorbent dosage, and the time of adsorption process on the dye removal percentage were investigated in detail. Based on the kinetic and thermodynamic studies, the adsorption process obeyed the pseudo-second order and Langmuir models, respectively. The obtained results revealed that the dye removal efficiency of CTS-SBA-15 was about 98% in the presence of 0.03 g of the adsorbent and pH = 7 after 80 min. So, it was found that CTS-SBA-15 can act as inexpensive and efficient adsorbent for the brilliant Red E-4BA elimination from the contaminated water.

Functionalized Ordered Mesoporous Silicas (MCM-41): Synthesis and Applications in Catalysis

Mesoporous silica sieves are among the most studied nano-objects due to their stable pore structure and easy preparation. In particular, MCM-41 have attracted increasing research attention due to their chemical versatility. This review focuses on the synthesis and regioselective functionalization of MCM-41 to prepare catalytic systems. The topics covered are: mono and di-functionalized MCM-41 as basic and acid catalysts, catalysts based on metallic complexes and heteropolyacids supported onto MCM-41, metallic nanoparticles embed onto functionalized MCM-41 and magnetic MCM-41 for catalytic purposes.

Mesoporous silica materials modified with aggregated transition metal species (Cr, Fe and Cr-Fe) in the role of catalysts for selective catalytic oxidation of ammonia to dinitrogen

Mesoporous silica sieves (SBA-15 and HMS) modified with propylsulfonic groups were used as supports for deposition of trinuclear acetate oligocations (Cr, Fe and Cr-Fe) by ion-exchange method. The obtained samples were characterized with respect to: textural parameters (low-temperature N2 adsorption), ordering of their porous structure (XRD), efficiency of organic functional groups anchoring (DRIFT, TG-DTG and elemental analysis), form and aggregation of deposited transition metal species (UV–vis-DRS), surface acidity (NH3-TPD), transition metal loadings (EDS microanalysis) and reducibility of deposited transition metal species (H2-TPR). The obtained samples were tested as catalysts for selective catalytic oxidation of ammonia by oxygen (NH3-SCO). Mesoporous silica supports modified with chromium and iron species were found to be active and selective catalysts in this process. Moreover, it was shown that the samples doped with mixed-metal oligocations (Cr2Fe1 or Cr1Fe2) were characterized by better catalytic activity in comparison to the samples modified with monometallic species (Cr3 or Fe3).

Development of Amperometric Laccase Biosensor through Immobilizing Enzyme in Magnesium‐Containing Mesoporous Silica Sieve (Mg‐MCM‐41)/Polyvinyl Alcohol Matrix

Magnesium‐containing mesoporous silica sieve (Mg‐MCM‐41) provided a suitable immobilization of biomolecule matrix due to its uniform pore structure, high surface areas, fast electron‐transfer rate, and good biocompatibility. Based on this, an amperometric biosensor was developed by entrapping laccase into the Mg‐MCM‐41/PVA composite matrix. Laccase from Trametes versicolor was assembled on a composite film of Mg‐MCM‐41/PVA modified Au electrode and the electrode was investigated by cyclic voltammetry, impedance spectroscopy, and chronoamperometry. The results indicated that the Mg‐MCM‐41/PVA/Lac modified electrode exhibited excellent catalytic activity towards catechol at room temperature in pH 4.8 acetate buffer solution. The optimum experimental conditions of biosensor for the detection of catechol were studied in detail. Under the optimal conditions, the linear range was from 0.94 to 10.23 μM with the sensitivity of 16.9227 A/M, the detection limit of 0.00531 μM, and the response time of less than 14 s. The Michaelis‐Menten constant () was estimated by Lineweaver‐Burk equation and the value was about 1.01 μM. In addition, the biosensor exhibited high reproducibility and long‐time stability. This work demonstrated that Mg‐MCM‐41/PVA composite provides a suitable support for laccase immobilization and construction of biosensor.

Direct Electrochemistry and Electrocatalysis of Hemoglobin on Bimetallic Au–Pt Inorganic–Organic Nanofiber Hybrid Nanocomposite and Mesoporous Molecular Sieve MCM-41

A glassy carbon electrode modified with MCM-41 and bimetallic inorganic–organic nanofiber hybrid nanocomposite was prepared and used for determination of trace levels of hydrogen peroxide (H2O2). The direct electron transfer (DET) and electrocatalysis of hemoglobin (Hb) entrapped in the MCM-41 modified Au–Pt inorganic–organic nanofiber hybrid nanocomposite electrode (Au–PtNP/NF/GCE) were investigated by using cyclic voltammetry in 0.1 M pH 7.0 phosphate buffer solution. Due to its uniform pore structure, high surface area and good biocompatibility, the mesoporous silica sieve MCM-41 provided a suitable matrix for immobilization of biomolecules. The MCM-41 modified Au–Pt inorganic–organic nanofiber hybrid nanocomposite electrode showed significant promotion to DET of Hb, which exhibited a pair of well-defined and quasi-reversible peaks for heme Fe(III)/Fe(II) with a formal potential of −0.535 V (vs. Ag/AgCl). Additionally, the Hb immobilized on the MCM-41 modified electrode showed excellent electrocatalytic activity toward H2O2 reduction.

Impacts of meso-structure and organic loadings of fluoroalcohol derivatives/SBA-15 hybrids on nerve agent simulant sensing

This paper employed a measurement of quartz crystal microbalance (QCM) to investigate the effects of mesopore structures and amount of organic loadings of fluoroalcohol derivatives/SBA-15 (a kind of ordered mesoporous silica sieve) hybrids on the sensing behavior of nerve agent simulant DMMP (dimethyl methylphosphonate). The meso-structure and functional groups of silica-based mesoporous hybrids were examined by SAXS, TEM, N2 adsorption–desorption isotherms and elemental analysis. The results show that much higher response value and sensitivity are achieved when the hybrid materials have relative higher pore volume and surface area. However, this effect only appears when the mesoporous hybrids have well-ordered porous structure, indicating that ordered meso-structure is critical in fabricating high-performance DMMP sensors. The reason is likely that the ordered meso-structure not only provides a larger number of contactable HFIP groups, but also facilitates molecules diffusion in porous structure. On the other hand, the specific interaction between HFIP/SBA-15 hybrids and DMMP vapor is greatly enhanced as the amount of fluoroalcohol derivatives increases. Therefore, the amount of organic functional groups incorporated plays an important role in determining the selectivity of sensors.

Direct electrochemistry and electrocatalytic properties of hemoglobin immobilized on a carbon ionic liquid electrode modified with mesoporous molecular sieve MCM-41

The direct electron transfer and electrocatalysis of hemoglobin (Hb) entrapped in the MCM-41 modified carbon ionic liquid electrode (CILE) were investigated by using cyclic voltammetry in 0.10 M pH 7.0 phosphate buffer solution (PBS). Due to its uniform pore structure, high surface areas and good biocompatibility, the mesoporous silica sieve MCM-41 provided a suitable matrix for immobilization of biomolecule. The MCM-41 modified CILE showed significant promotion to the direct electron transfer of Hb, which exhibited a pair of well defined and quasi-reversible peaks for heme Fe(III)/Fe(II) with a formal potential of −0.284 V (vs. Ag/AgCl). Additionally, the Hb immobilized on the MCM-41 modified carbon ionic liquid electrode showed excellent electrocatalytic activity toward H 2O 2. The electrocatalytic current values were linear with increasing concentration of H 2O 2 in a wide range of 5–310 μM and the corresponding detection limit was calculated to be 5 × 10 −8 M (S/N = 3). The surface coverage of Hb immobilized on the MCM-41 modified carbon ionic liquid electrode was about 2.54 × 10 −9 mol cm −2. The Michaelis–Menten constant K m app of 214 μM indicated that the Hb immobilized on the modified electrode showed high affinity to H 2O 2. The proposed electrode had high stability and good reproducibility due to the protection effect of MCM-41 and ionic liquid, and it would have wide potential applications in direct electrochemistry, biosensors and biocatalysis.

Laccase immobilized on methylene blue modified mesoporous silica MCM-41/PVA

The mesoporous silica sieve MCM-41 containing methylene blue (MB) provides a suitable immobilization of biomolecule matrix due to its uniform pore structure, high surface areas, good biocompatibility and nice conductivity. Based on this, a facilely fabricated amperometric biosensor by entrapping laccase into the MB modified MCM-41/PVA composite film has been developed. Laccase from Trametes versicolor is assembled on a composite film of MCM-41 containing MB/PVA modified Au electrode and the electrode is characterized with respect to transmission electron microscopy (TEM) and scanning electron microscopic (SEM), Cyclic voltammetry (CV), response time, detection limit, linear range and activity of laccase. The laccase modified electrode remains good redox behavior in pH 4.95 acetate buffer solution, at room temperature in present of 0.1 mM catechol. The response time ( t 90%) of the modified electrode is less than 4 s for catechol. The detection limit is 0.331 µM and the linear detect range is about from 4.0 µM to 87.98 µM for catechol with a correlation coefficient of 0.99913( S/ N = 3). The apparent Michaelis–Menten ( K M app ) is estimated using the Lineweaver–Burk equation and the K M app value is about 0.256 mM. This work demonstrated that the mesoporous silica MCM-41 containing MB provides a novel support for laccase immobilization and the construction of biosensors with a faster response and better bioactivity.

Temperature dependence of positronium lifetime in cylindrical pores

AbstractPositron Annihilation Lifetime Spectroscopy (PALS) results for ordered mesoporous silica sieves (MCM‐41 and its fibre form MSF) are used to verify predictions of the Extended Tao‐Eldrup (ETE) model. Cylindrical pores (R ∼ 1–2 nm) in these materials have well defined geometry and size, thus the structure of MCM‐41 and MSF reproduces the model assumptions. Positron lifetimes were measured in the range 100‐500K. In MCM‐41, due to low intensity of pore related ortho‐positronium component, it is difficult to determine the component's lifetime precisely. Accuracy of the lifetime fitting is better for MSF, where temperature dependence is in a good agreement with the ETE model results. For comparison, the ETE model predictions fit the lifetime of the pore related component in the Vycor sample only for T &gt; 200 K. Below this value the lifetime exceeds the model predictions by over 30%. (© 2007 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Nanoparticle separation by mesoporous molecular sieves

A separation technique based on the size-selective adsorption of nanoparticles by mesoporous silica sieves is proposed, which provides a narrow size distribution of PbSe nanocrystals incorporated into the pores.